Method and system for a vertical junction high-speed phase modulator

ABSTRACT

Methods and systems for a vertical junction high-speed phase modulator are disclosed and may include a semiconductor device having a semiconductor waveguide including a slab section, a rib section extending above the slab section, and raised ridges extending above the slab section on both sides of the rib section. The semiconductor device has a vertical pn junction with p-doped material and n-doped material arranged vertically with respect to each other in the rib and slab sections. The rib section may be either fully n-doped or p-doped in each cross-section along the semiconductor waveguide. Electrical connection to the p-doped and n-doped material may be enabled by forming contacts on the raised ridges, and electrical connection may be provided to the rib section from one of the contacts via periodically arranged sections of the semiconductor waveguide, where a cross-section of both the rib section and the slab section in the periodically arranged sections may be fully n-doped or fully p-doped.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application is a continuation of pending U.S. application Ser. No.16/206,749 filed Nov. 30, 2018, which is a divisional of U.S.application Ser. No. 15/694,236 filed on Sep. 1, 2017 and issued as U.S.Pat. No. 10,444,593 on Oct. 15, 2019, which claims priority to and thebenefit of U.S. Provisional Application 62/382,326 filed on Sep. 1,2016, which is hereby incorporated herein by reference in its entirety.

FIELD

Aspects of the present disclosure relate to electronic components. Morespecifically, certain implementations of the present disclosure relateto methods and systems for a vertical junction high-speed phasemodulator.

BACKGROUND

Conventional approaches for high-speed phase modulators may be costly,cumbersome, and/or inefficient—e.g., they may be complex and/or timeconsuming, and/or may introduce asymmetry.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present disclosureas set forth in the remainder of the present application with referenceto the drawings.

BRIEF SUMMARY

System and methods are provided for a vertical junction high-speed phasemodulator, substantially as shown in and/or described in connection withat least one of the figures, as set forth more completely in the claims.

These and other advantages, aspects and novel features of the presentdisclosure, as well as details of an illustrated embodiment thereof,will be more fully understood from the following description anddrawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a block diagram of a photonically-enabled integrated circuitwith a vertical junction high-speed phase modulator, in accordance withan example embodiment of the disclosure.

FIG. 1B is a diagram illustrating an exemplary photonically-enabledintegrated circuit, in accordance with an example embodiment of thedisclosure.

FIG. 1C is a diagram illustrating a photonically-enabled integratedcircuit coupled to an optical fiber cable, in accordance with an exampleembodiment of the disclosure.

FIG. 2A is a schematic illustrating an electro-optic modulator, inaccordance with an example embodiment of the disclosure.

FIG. 2B illustrates a cross-section view of a phase modulating region,in accordance with an example embodiment of the disclosure.

FIGS. 3A-3C illustrate an optical mode in a vertical HSPM junction andalternative contacting schemes, in accordance with an embodiment of thedisclosure.

FIG. 4 illustrates an example connection scheme for a vertical junctionHSPM, in accordance with an example embodiment of the disclosure.

FIG. 5 illustrates another example connection scheme for a verticaljunction HSPM, in accordance with an example embodiment of thedisclosure.

FIG. 6 illustrates yet another example connection scheme for a verticaljunction HSPM, in accordance with an example embodiment of thedisclosure.

FIG. 7 illustrates yet another example connection scheme for a verticaljunction HSPM, in accordance with an example embodiment of thedisclosure.

FIG. 8 illustrates yet another example connection scheme for a verticaljunction HSPM, in accordance with an example embodiment of thedisclosure.

FIG. 9 illustrates an alternating vertical junction/horizontal junctionHSPM, in accordance with an example embodiment of the disclosure.

FIG. 10 illustrates another embodiment of an alternating verticaljunction/lateral junction HSPM, in accordance with an example embodimentof the disclosure.

DETAILED DESCRIPTION OF THE INVENTION

As utilized herein the terms “circuits” and “circuitry” refer tophysical electronic components (i.e. hardware) and any software and/orfirmware (“code”) which may configure the hardware, be executed by thehardware, and or otherwise be associated with the hardware. As usedherein, for example, a particular processor and memory may comprise afirst “circuit” when executing a first one or more lines of code and maycomprise a second “circuit” when executing a second one or more lines ofcode. As utilized herein, “and/or” means any one or more of the items inthe list joined by “and/or”. As an example, “x and/or y” means anyelement of the three-element set {(x), (y), (x, y)}. In other words, “xand/or y” means “one or both of x and y”. As another example, “x, y,and/or z” means any element of the seven-element set {(x), (y), (z), (x,y), (x, z), (y, z), (x, y, z)}. In other words, “x, y and/or z” means“one or more of x, y and z”. As utilized herein, the term “exemplary”means serving as a non-limiting example, instance, or illustration. Asutilized herein, the terms “e.g.,” and “for example” set off lists ofone or more non-limiting examples, instances, or illustrations. Asutilized herein, circuitry or a device is “operable” to perform afunction whenever the circuitry or device comprises the necessaryhardware and code (if any is necessary) to perform the function,regardless of whether performance of the function is disabled or notenabled (e.g., by a user-configurable setting, factory trim, etc.).

FIG. 1A is a block diagram of a photonically-enabled integrated circuitwith a vertical junction high-speed phase modulator, in accordance withan example embodiment of the disclosure. Referring to FIG. 1A, there isshown optoelectronic devices on a photonically-enabled integratedcircuit 130 comprising optical modulators 105A-105D, photodiodes111A-111D, monitor photodiodes 113A-113H, and optical devices comprisingcouplers 103A-103K, optical terminations 115A-115D, and grating couplers117A-117H. There are also shown electrical devices and circuitscomprising amplifiers 107A-107D, analog and digital control circuits109, and control sections 112A-112D. The amplifiers 107A-107D maycomprise transimpedance and limiting amplifiers (TIA/LAs), for example.

In an example scenario, the photonically-enabled integrated circuit 130comprises a CMOS photonics die with a laser assembly 101 coupled to thetop surface of the IC 130. The laser assembly 101 may comprise one ormore semiconductor lasers with isolators, lenses, and/or rotators fordirecting one or more CW optical signals to the coupler 103A. Thephotonically enabled integrated circuit 130 may comprise a single chip,or may be integrated on a plurality of die, such as one or moreelectronics die and one or more photonics die.

Optical signals are communicated between optical and optoelectronicdevices via optical waveguides 110 fabricated in thephotonically-enabled integrated circuit 130. Single-mode or multi-modewaveguides may be used in photonic integrated circuits. Single-modeoperation enables direct connection to optical signal processing andnetworking elements. The term “single-mode” may be used for waveguidesthat support a single mode for each of the two polarizations,transverse-electric (TE) and transverse-magnetic (TM), or for waveguidesthat are truly single mode and only support one mode whose polarizationis TE, which comprises an electric field parallel to the substratesupporting the waveguides. Two typical waveguide cross-sections that areutilized comprise strip waveguides and rib waveguides. Strip waveguidestypically comprise a rectangular cross-section, whereas rib waveguidescomprise a rib section on top of a waveguide slab. Of course, otherwaveguide cross section types are also contemplated and within the scopeof the disclosure.

In an example scenario, the couplers 103A-103C may comprise low-lossY-junction power splitters where coupler 103A receives an optical signalfrom the laser assembly 101 and splits the signal to two branches thatdirect the optical signals to the couplers 103B and 103C, which splitthe optical signal once more, resulting in four roughly equal poweroptical signals.

The optical power splitter may comprise at least one input waveguide andat least two output waveguides. The couplers 103A-103C shown in FIG. 1Aillustrates 1-by-2 splitters, which divide the optical power in onewaveguide into two other waveguides evenly. These Y-junction splittersmay be used in multiple locations in an optoelectronic system, such asin a Mach-Zehnder interferometer (MZI) modulator, e.g., the opticalmodulators 105A-105D, where a splitter and a combiner are needed, sincea power combiner can be a splitter used in reverse.

In another example scenario, the Y-junction may be utilized in aparallel multi-channel transmitter, where a cascade of 1-by-2 splitterscan be employed to have a single light source feed multiple channels.Interleaver-based multiplexers and demultiplexers constitute a thirdexample where 1-by-2 splitters are among the building blocks.

The optical modulators 105A-105D comprise Mach-Zehnder or ringmodulators, for example, and enable the modulation of thecontinuous-wave (CW) laser input signal. The optical modulators105A-105D may comprise high-speed and low-speed phase modulationsections and are controlled by the control sections 112A-112D. Thehigh-speed phase modulation section of the optical modulators 105A-105Dmay modulate a CW light source signal with a data signal. The low-speedphase modulation section of the optical modulators 105A-105D maycompensate for slowly varying phase factors such as those induced bymismatch between the waveguides, waveguide temperature, or waveguidestress and is referred to as the passive phase, or the passive biasingof the MZI.

In an example scenario, the high-speed optical phase modulators mayoperate based on the free carrier dispersion effect and may demonstratea high overlap between the free carrier modulation region and theoptical mode. High-speed phase modulation of an optical mode propagatingin a waveguide is the building block of several types of signal encodingused for high data rate optical communications. Speed in the tens ofGb/s may be required to sustain the high data rates used in modernoptical links and can be achieved in integrated Si photonics bymodulating the depletion region of a PN junction placed across thewaveguide carrying the optical beam. In order to increase the modulationefficiency and minimize the loss, the overlap between the optical modeand the depletion region of the PN junction is optimized.

The outputs of the optical modulators 105A-105D may be optically coupledvia the waveguides 110 to the grating couplers 117E-117H. The couplers103D-103K may comprise four-port optical couplers, for example, and maybe utilized to sample or split the optical signals generated by theoptical modulators 105A-105D, with the sampled signals being measured bythe monitor photodiodes 113A-113H. The unused branches of thedirectional couplers 103D-103K may be terminated by optical terminations115A-115D to avoid back reflections of unwanted signals.

The grating couplers 117A-117H comprise optical gratings that enablecoupling of light into and out of the photonically-enabled integratedcircuit 130. The grating couplers 117A-117D may be utilized to couplelight received from optical fibers into the photonically-enabledintegrated circuit 130, and the grating couplers 117E-117H may beutilized to couple light from the photonically-enabled integratedcircuit 130 into optical fibers. The grating couplers 117A-117H maycomprise single polarization grating couplers (SPGC) and/or polarizationsplitting grating couplers (PSGC). In instances where a PSGC isutilized, two input, or output, waveguides may be utilized.

The optical fibers may be epoxied, for example, to the CMOS chip, andmay be aligned at an angle from normal to the surface of thephotonically-enabled integrated circuit 130 to optimize couplingefficiency. In an example embodiment, the optical fibers may comprisesingle-mode fiber (SMF) and/or polarization-maintaining fiber (PMF).

In another exemplary embodiment illustrated in FIG. 1B, optical signalsmay be communicated directly into the surface of thephotonically-enabled integrated circuit 130 without optical fibers bydirecting a light source on an optical coupling device in the chip, suchas the light source interface 135 and/or the optical fiber interface139. This may be accomplished with directed laser sources and/or opticalsources on another chip flip-chip bonded to the photonically-enabledintegrated circuit 130.

The photodiodes 111A-111D may convert optical signals received from thegrating couplers 117A-117D into electrical signals that are communicatedto the amplifiers 107A-107D for processing. In another embodiment of thedisclosure, the photodiodes 111A-111D may comprise high-speedheterojunction phototransistors, for example, and may comprise germanium(Ge) in the collector and base regions for absorption in the 1.3-1.6 μmoptical wavelength range, and may be integrated on a CMOSsilicon-on-insulator (SOI) wafer.

In the receiver subsystem implemented in a silicon chip, light is oftencoupled into a photodetector via a polarization-splitting gratingcoupler that supports coupling all polarization states of the fiber modeefficiently. The incoming signal is split by the PSGC into two separatewaveguides in a polarization-diversity scheme, and therefore both inputsto the waveguide photodetectors are used.

The analog and digital control circuits 109 may control gain levels orother parameters in the operation of the amplifiers 107A-107D, which maythen communicate electrical signals off the photonically-enabledintegrated circuit 130. The control sections 112A-112D compriseelectronic circuitry that enable modulation of the CW laser signalreceived from the splitters 103A-103C. The optical modulators 105A-105Dmay require high-speed electrical signals to modulate the refractiveindex in respective branches of a Mach-Zehnder interferometer (MZI), forexample.

In operation, the photonically-enabled integrated circuit 130 may beoperable to transmit and/or receive and process optical signals. Opticalsignals may be received from optical fibers by the grating couplers117A-117D and converted to electrical signals by the photodetectors111A-111D. The electrical signals may be amplified by transimpedanceamplifiers in the amplifiers 107A-107D, for example, and subsequentlycommunicated to other electronic circuitry, not shown, in thephotonically-enabled integrated circuit 130.

Integrated photonics platforms allow the full functionality of anoptical transceiver to be integrated on a single chip. An opticaltransceiver chip contains optoelectronic circuits that create andprocess the optical/electrical signals on the transmitter (Tx) and thereceiver (Rx) sides, as well as optical interfaces that couple theoptical signals to and from a fiber. The signal processing functionalitymay include modulating the optical carrier, detecting the opticalsignal, splitting or combining data streams, and multiplexing ordemultiplexing data on carriers with different wavelengths, andequalizing signals for reducing and/or eliminating inter-symbolinterference (ISI), which may be a common impairment in opticalcommunication systems.

Optical modulators may be used to impart a data signal onto a CW opticalsignal. Rib waveguide sections with integrated PN junctions may beutilized in MZI modulators, and are shown further with respect to FIGS.2-10 .

FIG. 1B is a diagram illustrating an exemplary photonically-enabledintegrated circuit, in accordance with an example embodiment of thedisclosure. Referring to FIG. 1B, there is shown thephotonically-enabled integrated circuit 130 comprising electronicdevices/circuits 131, optical and optoelectronic devices 133, a lightsource interface 135, a chip front surface 137, an optical fiberinterface 139, CMOS guard ring 141, and a surface-illuminated monitorphotodiode 143.

The light source interface 135 and the optical fiber interface 139comprise grating couplers, for example, that enable coupling of lightsignals via the CMOS chip surface 137, as opposed to the edges of thechip as with conventional edge-emitting/receiving devices. Couplinglight signals via the chip surface 137 enables the use of the CMOS guardring 141 which protects the chip mechanically and prevents the entry ofcontaminants via the chip edge.

The electronic devices/circuits 131 comprise circuitry such as theamplifiers 107A-107D and the analog and digital control circuits 109described with respect to FIG. 1A, for example. The optical andoptoelectronic devices 133 comprise devices such as the couplers103A-103K, optical terminations 115A-115D, grating couplers 117A-117H,optical modulators 105A-105D, high-speed heterojunction photodiodes111A-111D, and monitor photodiodes 113A-113H.

FIG. 1C is a diagram illustrating a photonically-enabled integratedcircuit coupled to an optical fiber cable, in accordance with an exampleembodiment of the disclosure. Referring to FIG. 1C, there is shown thephotonically-enabled integrated circuit 130 comprising the chip surface137, and the CMOS guard ring 141. There is also shown a fiber-to-chipcoupler 145, an optical fiber cable 149, and an optical source assembly147.

The photonically-enabled integrated circuit 130 comprises the electronicdevices/circuits 131, the optical and optoelectronic devices 133, thelight source interface 135, the chip surface 137, and the CMOS guardring 141 may be as described with respect to FIG. 1B.

In an example embodiment, the optical fiber cable may be affixed, viaepoxy for example, to the CMOS chip surface 137. The fiber chip coupler145 enables the physical coupling of the optical fiber cable 149 to thephotonically-enabled integrated circuit 130. In another examplescenario, the IC 130 may comprise photonic devices on one die, such as aphotonics interposer, and electrical devices on an electronics die, bothof which may comprise CMOS die.

FIG. 2A is a schematic illustrating an electro-optic modulator, inaccordance with an example embodiment of the disclosure. Referring toFIG. 2A, there is shown an optical modulator 200 comprising opticalwaveguides 201A and 201B and optical phase shifters 203A and 203B. Thereis also shown an input signal P_(in) 205 and output signals P_(out) 207Aand 207B.

The waveguides 201A and 201B may comprise materials of differingdielectric constants such that optical signals are confined. Forexample, a silicon waveguide with air and/or silicon dioxide claddingmay carry optical signals and may come into close proximity at twolocations in the optical modulator 200 as shown in FIG. 2A, which mayresult in a transfer of a portion of the optical mode from one waveguideto the other.

The optical phase shifters 203A and 203B may comprise optoelectronicdevices that may be operable to shift the phase of received opticalsignals. For example, p-n junctions formed in the waveguides 201A and201B may be utilized to shift the phase of optical signals that travelthrough the depletion region, since the index of refraction is changedwith respect to the non-depleted regions of the waveguides.Reverse-biased p-n junctions result in an increased depletion width andthus more phase shift.

Optical modulation amplitude (OMA) is one of the key performanceparameters of an electro-optic phase modulator used in digitalcommunication systems. The OMA directly influences the system bit errorrate (BER) and hence is desired to be as large as possible. In bi-leveloptical signaling schemes, the higher level represents a binary one, andthe lower power level represents a zero (maximum and minimum of P_(out)in FIG. 2A). OMA is defined as the difference between the high and lowlevels: OMA=max(P_(out))−min(P_(out)).

The magnitude of OMA depends on phase shift difference accumulatedbetween the two arms, waveguides 201A and 201B, of the optical modulator200 as well as the optical loss that the beam suffers passing throughthe waveguides. The following equation describes this relation:OMA(L)=P _(in) e ^(−α·L) sin(θ·L)where P_(in) is the input optical power, α is the optical loss per unitlength, L is the length of the modulator and θ is the difference inphase shift between two arms per unit length. As can be seen from therelation, OMA increases with increasing phase shift and decreases byincreasing loss. As a result, there is an optimal modulator length,beyond which the OMA no longer improves.

FIG. 2B illustrates a cross-section view of a phase modulating region,in accordance with an example embodiment of the disclosure. Referring toFIG. 2B, there is shown a rib waveguide phase shifter 203, where theupper view shows the optical mode 225 in the rib 211 and slab section212 of the n-doped region 219 and p-doped region 221, and the lower viewshows the p- and n-doped regions 219 and 221 in the rib and slab regions211 and 212. There is also shown contacts 215 formed on outer ribs 217separated from the rib waveguide by trenches 213.

The high-speed phase modulator (HSPM) 203 is formed where the p- andn-doped regions meet, resulting in the depletion region 223 at theinterface of the n-doped region 219 and p-doped region 221. In thisconfiguration, there is good overlap of the depletion region 223 withthe optical mode 225, which results in good efficiency, when thejunction is near the waveguide center. Electrical connection of eachside of the junction occurs via p/n-doped regions extending through theslab region. The HSPM modulates the phase and loss of the optical modein the waveguide, as a function of bias on the contacts.

FIGS. 3A-3C illustrate an optical mode in a vertical HSPM junction andalternative contacting schemes, in accordance with an embodiment of thedisclosure. Referring to FIG. 3A, there is shown an optical mode in therib waveguide and slab regions of a HSPM. With a vertical junction,where the electric fields in the depletion region are oriented in avertical direction, there is increased efficiency due to a betteroverlap between the optical mode and the depletion region. However,electrical connection to such a structure may be difficult for avertical junction.

FIG. 3B illustrates a possible contact scenario, with n-doped region301, p-doped region 303, n-region contact 305, p-region contact 307, anda depletion region 309 where the electric fields are oriented verticallyand the n-region contact 305 is placed on the top of the rib. However,metal in the n-region contact 305 interacts with the optical mode andmay significantly increase optical loss, offsetting the gain inefficiency of the vertical junction.

FIG. 3C illustrates another possible contact scenario, with n-dopedregion 311, p-doped region 313, n-region contact 315, p-region contact317, and a depletion region 311 where the electric fields are orientedvertically and horizontally in an “L” shape. In this embodiment, thecontacts 315 and 317 are made on n-doped and p-doped slab sections wherethe n-doped region 311 extends into the rib, reducing the length of thevertical junction depletion region 319. This “neck” region connectingthe rib and slab portions of the n-doped region 311 results in increasedresistance between the n-region contact 315 to the n-side of the PNjunction, thereby reducing the modulation bandwidth. Furthermore, thewider the neck region, the shorter the vertical junction portion, whichreduces modulation efficiency. Therefore a low-loss and low-resistanceelectrical connectivity may be difficult while retaining an efficientvertical junction.

FIG. 4 illustrates an example connection scheme for a vertical junctionHSPM, in accordance with an example embodiment of the disclosure.Referring to FIG. 4 , there is shown an oblique angle view of HSPM 400with two cross-sectional views at different locations along the ribwaveguide, as indicated by the arrows from the dotted lines in theoblique view directed towards the corresponding cross-sectional view.

In the embodiment shown, the junction configuration is varied along thewaveguide, such that the top of the waveguide is completely n-doped, forexample, through its length, where n-doped region 401 extends the entirelength of the rib 411. Most of the bottom of the waveguide, in the slabsection 412, is p-doped region 403, and extends the entire length of theslab 412 except for narrow regions to contact the n-doped region 401 ontop. This is illustrated by the upper left image corresponding to one ofthe narrow stripes of n-doping in the slab region in addition to therib, whereas the upper right view represents the rest of the length ofthe structure. In another example scenario, the p- and n-doped regionsmay be reversed with n-doped slab 412 and p-doped rib 411.

The “unit length” in the oblique view indicates the spacing betweenn-contact regions 405, and the contact region width is also indicated,both of which may be configured to trade off modulation efficiency,resistance, and bandwidth, for example. The p-region contacts 407 may beplaced at the midpoint between the n-region contacts 405, also withvarying width. The contact regions may be interspersed periodically, asin at regular distances, or in varying distances along the length of thewaveguide.

FIG. 5 illustrates another example connection scheme for a verticaljunction HSPM, in accordance with an example embodiment of thedisclosure. Referring to FIG. 5 , there is shown an oblique angle viewof HSPM 500 with four cross-sectional views at different locations alongthe rib waveguide, as indicated by the arrows. There is also shownwaveguide 510 comprising rib 511 and slab 512, which comprise n-dopedregion 501, p-doped region 503, n-region contact 505, and p-regioncontact 507.

In the embodiment shown, the junction configuration is varied along thewaveguide 510, such that the rib 511 of the waveguide 510 is alternatelydoped n-type and p-type through its length, while the slab 512, isalternately doped p-type and n-type along the length of the waveguide510. This is illustrated by the upper left and upper rightcross-sectional views corresponding to the alternating doping of the rib511, where the rib 511 is p-type in one section and n-type in the other.

The lower left and lower right cross-sectional views illustrate thecontacting regions, which may be situated periodically along the lengthat interfaces between the alternating doped regions, with narrow stripesof uniform n-doping electrically coupling n-doped slab regions ton-doped rib sections, as illustrated in the lower left view, and narrowstripes of uniform p-doping electrically coupling p-doped slab regionsto p-doped rib sections, as illustrated in the lower right view.

The “unit length” indicates the spacing between alternating dopedregions, and the contact region width is also indicated, both of whichmay be configured to trade off modulation efficiency, resistance, andbandwidth, for example. The contact regions may be interspersedperiodically, as in at regular distances, or in varying distances alongthe length of the waveguide.

FIG. 6 illustrates yet another example connection scheme for a verticaljunction HSPM, in accordance with an example embodiment of thedisclosure. Referring to FIG. 6 , there is shown an oblique angle viewof HSPM 600 with two cross-sectional views at different locations alongthe rib waveguide, as indicated by the dashed lines. There is also shownwaveguide 610 comprising rib 611 and slab 612, which comprise n-dopedregion 601, p-doped region 603, n-region contact 605, p-region contact607, and i-region 613. The i-region comprises a nominally undoped, orintrinsic, region.

In the embodiment shown, the junction configuration is varied along thewaveguide 610, such that the top of the waveguide 610 is completelyn-doped, for example, through its length, while most of the bottom ofthe waveguide, in the slab section 612, is p-doped except for narrowregions to contact the n-region on top. This is illustrated by the upperleft image corresponding to one of the narrow stripes of n-doping in theslab region 612 in addition to the rib 611. In addition, on one side ofthe rib waveguide, (the p-side) most of the cladding is p-doped,connecting the p-doped bottom of the waveguide 610 to the p-doped ridge603A. The regions where the n-doped bottom of the waveguide would extendinto the p-side cladding may be left undoped, or intrinsic, as indicatedby the “I” region 613, to reduce loss and capacitance.

On the other side of the waveguide (the n-side) most of the cladding isundoped except for narrow regions of n-doping that connect the n-dopedtop of the waveguide to the n-doped ridge.

In another example scenario, the p- and n-doped regions may be reversedwith n-doped slab regions and p-doped rib.

As with previous embodiments, the contact region width and unit lengthbetween contact regions may be configured to trade off modulationefficiency, resistance, and bandwidth, for example. The contact regionsmay be interspersed periodically, as in at regular distances, or invarying distances along the length of the waveguide.

FIG. 7 illustrates yet another example connection scheme for a verticaljunction HSPM, in accordance with an example embodiment of thedisclosure. Referring to FIG. 7 , there is shown an oblique angle viewof HSPM 700 with three cross-sectional views at different locationsalong the rib waveguide, as indicated by the dashed lines. There is alsoshown waveguide 710 comprising rib 711 and slab 712, which comprisen-doped region 701, p-doped region 703, n-region contact 705, p-regioncontact 707, i-region 713, and low p-doped region 715. The i-region 713comprises a nominally undoped, or intrinsic, region.

In the embodiment shown, the junction configuration is varied along thewaveguide, such that the rib 711 of the waveguide 710 is completelyn-doped, for example, through its length, while most of the bottom ofthe waveguide, in the slab section 712, is p-doped except for narrowregions to contact the n-region on top. This is illustrated by the upperleft image corresponding to one of the narrow stripes of n-doping in theslab region in addition to the rib. In addition, on one side of the ribwaveguide, (the p-side) most of the cladding, i.e., the slab, isp-doped, connecting the p-doped bottom of the waveguide to the p-dopedridge 703A. The regions where the n-doped bottom of the waveguide wouldextend into the p-side cladding may be left undoped, or intrinsic, asindicated by the “I” region 713, to reduce loss and capacitance.

On the other side of the waveguide (the n-side) most of the cladding isundoped except for narrow regions of n-doping that connect the n-dopedtop of the waveguide to the n-doped ridge 701A. In addition, the dopingdensity in the bottom part of the waveguide can be different from thedoping density in the narrow contact regions, as indicated by the lowp-doped region 715.

In another example scenario, the p- and n-doped regions may be reversedwith n-doped slab regions and p-doped rib.

As with previous embodiments, the contact region width and unit lengthbetween contact regions may be configured to trade off modulationefficiency, resistance, and bandwidth, for example. The contact regionsmay be interspersed periodically, as in at regular distances, or invarying distances along the length of the waveguide.

FIG. 8 illustrates yet another example connection scheme for a verticaljunction HSPM, in accordance with an example embodiment of thedisclosure. Referring to FIG. 8 , there is shown an oblique angle viewof HSPM 800 with four cross-sectional views at different locations alongthe rib waveguide, as indicated by the dashed lines. There is also shownwaveguide 810 comprising rib 811 and slab 812, which comprise n-dopedregion 801, p-doped region 803, n-region contact 805, p-region contact807, and i-region 813. The i-region 713 comprises a nominally undoped,or intrinsic, region, for example.

In the embodiment shown, the junction configuration is varied along thewaveguide 810, such that the rib 811 of the waveguide is alternatelyn-doped and p-doped through its length, while the bottom of thewaveguide, in the slab section 812, alternates n-type 801 and intrinsicregions 813 while the other side of the rib 811 in the slab 812alternates between p-type 803 and intrinsic regions 813. The upper leftimage corresponds to an n-doped rib 811 and the upper right correspondsto a p-doped rib 811. The lower right images correspond to connectionregions where the rib and slab sections are commonly doped to provideelectrical connection to the rib 812.

As with previous embodiments, the contact region width and unit lengthbetween contact regions may be configured to trade off modulationefficiency, resistance, and bandwidth, for example. The contact regionsmay be interspersed periodically, as in at regular distances, or invarying distances along the length of the waveguide.

In making connections with vertical junctions, uniformly doped contactregions are introduced. To minimize series resistance, this contactregion should not be too narrow, but then this means that a certainfraction of the HSPM waveguide taken up by the contact region will notcontribute to phase shift, but will contribute to optical loss, loweringthe maximum achievable OMA.

In an alternative scenario, the HSPM may comprise subsequent verticaljunction and lateral junction regions. The lateral junction region maybe used to contact the vertical junction region but in itself alsoprovides phase shift. Moreover, an extra junction plane arisesperpendicular to the propagation direction of the light at the interfacebetween the lateral and vertical junction regions. This is shown furtherwith respect to FIGS. 9 and 10 .

FIG. 9 illustrates an alternating vertical junction/horizontal junctionHSPM, in accordance with an example embodiment of the disclosure.Referring to FIG. 9 , there is shown HSPM 900 comprising alternatinglateral junction and vertical junction regions. There is also shownwaveguide 910 comprising rib 911 and slab 912, which comprise n-dopedregion 901, p-doped region 903, n-region contact 905, and p-regioncontact 907, with alternating horizontal junctions 910 and verticaljunctions 920.

The top left image shows an oblique angle view of a unit cell of theHSPM 900 that is repeated along the light propagation direction. Ahorizontal junction 910 with p-doped region 903 on the left and n-dopedregion 901 on the right is shown and a vertical junction 920 withp-doped region 903 at bottom and n-doped region 901 on top is alsoshown, but a reverse configuration (p top/n bottom and n left/p right)or alternating both orientations is also possible.

FIG. 10 illustrates another embodiment of an alternating verticaljunction/lateral junction HSPM, in accordance with an example embodimentof the disclosure. Referring to FIG. 10 , there is shown HSPM 1000comprising alternating lateral junction and vertical junction regions.There is also shown n-doped region 1001, p-doped region 1003, n-regioncontact 1005, and p-region contact 1007, with alternating horizontaljunctions 1010 and vertical junctions 1020.

Referring to FIG. 10 , HSPM 1000 may be similar to HSPM 900, but part ofthe vertical junction 1020 top doping access region (n in this case) isleft undoped, as indicated by i-region 1011, to reduce capacitance. Inthis region, the rib 1011 comprises n-doped region 1001 and the slab1012 below comprises p-doped region 1003, such that the electric fieldsfrom the junction depletion region are oriented vertically.

In an example embodiment, a method and system are disclosed for avertical junction high-speed phase modulator. In this regard, aspects ofthe disclosure may comprise a semiconductor device having asemiconductor waveguide that comprises a slab section, a rib sectionextending above the slab section, and raised ridges extending above theslab section on both sides of the rib section. The semiconductor devicealso has a vertical pn junction with p-doped material and n-dopedmaterial arranged vertically with respect to each other in the rib andslab sections, where the rib section is either fully n-doped or fullyp-doped in each cross-section along the semiconductor waveguide. Thesemiconductor device further has an electrical connection to the p-dopedmaterial and n-doped material by forming contacts on the raised ridges,and an electrical connection to the rib section from one of the contactsvia periodically arranged sections of the semiconductor waveguide wherea cross-section of both the rib section and the slab section in theperiodically arranged sections is fully n-doped or fully p-doped.

The rib section may be fully n-doped or fully p-doped along a fulllength of the semiconductor waveguide. The rib section may alternatebetween fully p-doped or fully n-doped in sections along a full lengthof the semiconductor waveguide. The slab section may alternate betweenfully p-doped or fully n-doped in sections along a full length of thesemiconductor waveguide. The slab section may be fully n-doped or fullyp-doped along a full length of the semiconductor waveguide except for inthe periodically arranged sections. The raised ridges may be separatedfrom the rib by trenches. The semiconductor waveguide may comprise afirst phase modulation section of an optical modulator.

Other aspects of the disclosure may comprise a semiconductor devicehaving semiconductor waveguide comprising a slab section, a rib sectionextending above the slab section, and raised ridges extending above theslab section on both sides of the rib section. The semiconductor devicealso has a vertical pn junction with p-doped material and n-dopedmaterial arranged vertically with respect to each other in the rib andslab sections, respectively, where the rib section is either fullyn-doped or fully p-doped in each cross-section along the semiconductorwaveguide. The semiconductor device further has an electrical contact tothe p-doped material and n-doped material via contacts on the raisedridges and an electrical contact to the rib section from one of thecontacts via periodically arranged sections of the semiconductorwaveguide where a cross-section of both the rib section and the slabsection in the periodically arranged sections is mostly n-doped with anundoped portion or is mostly p-doped with an undoped portion.

Further aspects of the disclosure may comprise a semiconductor devicehaving a semiconductor waveguide comprising a slab section, a ribsection extending above the slab section, and raised ridges extendingabove the slab section on both sides of the rib section. A first portionof the semiconductor waveguide has a vertical pn junction with p-dopedmaterial and n-doped material arranged vertically with respect to eachother in the rib and slab sections, respectively, where the rib sectionis either fully n-doped or fully p-doped along the semiconductorwaveguide in the first portion. A second portion of the semiconductorwaveguide has a horizontal pn junction with p-doped material and n-dopedmaterial arranged laterally with respect to each other in both the riband slab sections. The semiconductor device also has an electricalcontact to the p-doped material and n-doped material via contacts on theraised ridges. A portion of the slab section in the second portion ofthe semiconductor waveguide may be undoped. The undoped portion of theslab section may be between the raised ridges and the rib section. Theraised ridges may be separated from the rib by trenches. Thesemiconductor waveguide may comprise a first phase modulation section ofan optical modulator.

While the present disclosure has been described with reference tocertain embodiments, it will be understood by those skilled in the artthat various changes may be made and equivalents may be substitutedwithout departing from the scope of the present invention. In addition,many modifications may be made to adapt a particular situation ormaterial to the teachings of the present invention without departingfrom its scope. Therefore, it is intended that the present invention notbe limited to the particular embodiment disclosed, but that the presentinvention will include all embodiments falling within the scope of theappended claims.

What is claimed is:
 1. A semiconductor device, the device comprising: asemiconductor waveguide comprising a slab section, a rib sectionextending above the slab section, and raised ridges extending above theslab section on both sides of the rib section; a first portion of thesemiconductor waveguide with a vertical pn junction with p-dopedmaterial and n-doped material arranged vertically with respect to eachother in the rib section and the slab section, respectively, wherein therib section is either fully n-doped or fully p-doped along thesemiconductor waveguide in the first portion; a second portion of thesemiconductor waveguide with a horizontal pn junction with p-dopedmaterial and n-doped material arranged laterally with respect to eachother in both the rib section and the slab section, wherein a portion ofthe slab section in the second portion of the semiconductor waveguide isundoped; and electrical contact to the p-doped material and n-dopedmaterial via contacts on the raised ridges.
 2. The device according toclaim 1, wherein the undoped portion of the slab section is between theraised ridges and the rib section.
 3. The device according to claim 1,wherein the raised ridges are separated from the rib section bytrenches.
 4. The device according to claim 3, wherein an undoped portionof the slab section is below one of the trenches.
 5. The deviceaccording to claim 1, wherein the semiconductor waveguide comprises afirst phase modulation section of an optical modulator.
 6. The deviceaccording to claim 1, wherein the semiconductor waveguide comprisessilicon.
 7. The device according to claim 1, wherein the semiconductorwaveguide is integrated in a complementary metal-oxide semiconductor(CMOS) die.
 8. A semiconductor device, the device comprising: asemiconductor waveguide comprising a slab section, a rib sectionextending above the slab section, and raised ridges extending above theslab section on both sides of the rib section, wherein the raised ridgesare separated from the rib section by trenches, and wherein an undopedportion of the slab section is below one of the trenches; a firstportion of the semiconductor waveguide with a vertical pn junction withp-doped material and n-doped material arranged vertically with respectto each other in the rib section and the slab section, respectively,wherein the rib section is either fully n-doped or fully p-doped alongthe semiconductor waveguide in the first portion; a second portion ofthe semiconductor waveguide with a horizontal pn junction with p-dopedmaterial and n-doped material arranged laterally with respect to eachother in both the rib section and the slab section; and electricalcontact to the p-doped material and n-doped material via contacts on theraised ridges.
 9. The device according to claim 8, wherein a portion ofthe slab section in the second portion of the semiconductor waveguide isundoped.
 10. The device according to claim 9, wherein the undopedportion of the slab section in the second portion of the semiconductorwaveguide is between the raised ridges and the rib section.
 11. Thedevice according to claim 8, wherein the semiconductor waveguidecomprises a first phase modulation section of an optical modulator. 12.The device according to claim 8, wherein the semiconductor waveguidecomprises silicon.
 13. The device according to claim 8, wherein thesemiconductor waveguide is integrated in a complementary metal-oxidesemiconductor (CMOS) die.
 14. A semiconductor device, the devicecomprising: a semiconductor waveguide comprising a slab section, a ribsection extending above the slab section, and raised ridges extendingabove the slab section on both sides of the rib section, wherein anundoped portion of the slab section is between the raised ridges and therib section; a first portion of the semiconductor waveguide with avertical pn junction with p-doped material and n-doped material arrangedvertically with respect to each other in the rib section and the slabsection, respectively, wherein the rib section is either fully n-dopedor fully p-doped along the semiconductor waveguide in the first portion;a second portion of the semiconductor waveguide with a horizontal pnjunction with p-doped material and n-doped material arranged laterallywith respect to each other in both the rib section and the slab section;and electrical contact to the p-doped material and n-doped material viacontacts on the raised ridges.
 15. The device according to claim 14,wherein a portion of the slab section in the second portion of thesemiconductor waveguide is undoped.
 16. The device according to claim14, wherein the raised ridges are separated from the rib section bytrenches.
 17. The device according to claim 16, wherein an undopedportion of the slab section is below one of the trenches.
 18. The deviceaccording to claim 14, wherein the semiconductor waveguide comprises afirst phase modulation section of an optical modulator.
 19. The deviceaccording to claim 14, wherein the semiconductor waveguide comprisessilicon.
 20. The device according to claim 14, wherein the semiconductorwaveguide is integrated in a complementary metal-oxide semiconductor(CMOS) die.